1. Field of the Invention
The invention relates in general to a frequency adjusting method and apparatus, and more particularly to a frequency adjusting method of a clock/data recovery (CDR) circuit and apparatus thereof.
2. Description of the Related Art
The conventional interface standard of parallel advanced technology attachment (PATA) is a kind of parallel data processing and is very inconvenient in usage owing that it has a great amount of wiring to occupy much space and its cables are too short to transmit stable signals. Therefore, due to requirements of convenience, stability and operational frequency, serial advanced technology attachment (SATA) has developed as a new generation of interface standard between a system and hard disk and will be designed to have an operational frequency of 6 Gbps in a scenario of technology development.
In the present market, the SATA-related product has a specification of STAT 1.0 and has an operational frequency of 1.5 Gbps. The new-generation SATA II has an operational frequency of 3 Gbps. When the two generations of products are connected for transmitting data, there usually comes out a problem due to different operational frequencies. For example, when a SATA 1.0 apparatus is used as a receiver and an SATA II apparatus is used as a transmitter for transmitting data to the receiver, due to different operational frequencies of the two apparatuses, the clock/data recovery (CDR) circuit in the lower-frequency receiver will follow the operational frequency of the transmitter. After a period of time, the frequency of the CDR circuit will go over an allowed operational range, be even locked to the operational frequency of the transmitter, and be unable to return to its own frequency.
When the SATA specification is changing between generations, connection between apparatuses of different SATA generations must result in problems due to their different operational frequencies. How to avoid an abnormal operation of the receiver apparatus due to frequency dispersion is an essential subject for a SATA product designer.